Mercurial > dropbear
view libtommath/bn_mp_radix_size.c @ 1790:42745af83b7d
Introduce extra delay before closing unauthenticated sessions
To make it harder for attackers, introduce a delay to keep an
unauthenticated session open a bit longer, thus blocking a connection
slot until after the delay.
Without this, while there is a limit on the amount of attempts an attacker
can make at the same time (MAX_UNAUTH_PER_IP), the time taken by dropbear to
handle one attempt is still short and thus for each of the allowed parallel
attempts many attempts can be chained one after the other. The attempt rate
is then:
"MAX_UNAUTH_PER_IP / <process time of one attempt>".
With the delay, this rate becomes:
"MAX_UNAUTH_PER_IP / UNAUTH_CLOSE_DELAY".
author | Thomas De Schampheleire <thomas.de_schampheleire@nokia.com> |
---|---|
date | Wed, 15 Feb 2017 13:53:04 +0100 |
parents | 1051e4eea25a |
children |
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line source
#include "tommath_private.h" #ifdef BN_MP_RADIX_SIZE_C /* LibTomMath, multiple-precision integer library -- Tom St Denis */ /* SPDX-License-Identifier: Unlicense */ /* returns size of ASCII representation */ mp_err mp_radix_size(const mp_int *a, int radix, int *size) { mp_err err; int digs; mp_int t; mp_digit d; *size = 0; /* make sure the radix is in range */ if ((radix < 2) || (radix > 64)) { return MP_VAL; } if (MP_IS_ZERO(a)) { *size = 2; return MP_OKAY; } /* special case for binary */ if (radix == 2) { *size = (mp_count_bits(a) + ((a->sign == MP_NEG) ? 1 : 0) + 1); return MP_OKAY; } /* digs is the digit count */ digs = 0; /* if it's negative add one for the sign */ if (a->sign == MP_NEG) { ++digs; } /* init a copy of the input */ if ((err = mp_init_copy(&t, a)) != MP_OKAY) { return err; } /* force temp to positive */ t.sign = MP_ZPOS; /* fetch out all of the digits */ while (!MP_IS_ZERO(&t)) { if ((err = mp_div_d(&t, (mp_digit)radix, &t, &d)) != MP_OKAY) { goto LBL_ERR; } ++digs; } /* return digs + 1, the 1 is for the NULL byte that would be required. */ *size = digs + 1; err = MP_OKAY; LBL_ERR: mp_clear(&t); return err; } #endif